This biogeographical study documents the modern distribution of ostracodes in the southwest Yukon Territory and northern British Columbia, Canada. The study tested the hypothesis that dissolved ion composition and concentrations of the lake water are the primary determinants of the distribution of modern ostracodes in this region. A total of 28 freshwater species representing 8 genera were identified in the 33 study lakes. Species common in the southwest Yukon are widely distributed throughout North America, and include Cyclocypris ampla , Candona candida , Cypria turneri , Cypria ophtalmica , and Candona protzi . Concentrations of ostracode valves were highest in four lakes with moderate conductivity values ranging between 330 and [...]